The present invention relates to an improved polymer optical fiber and a process and apparatus for making the improved polymer optical fiber. The invention includes a graded index polymer optical fiber and a process for the manufacture of a graded index polymer optical fiber. The invention also includes an optical fiber or polymer that is capable of shifting the wavelength of the incoming electromagnetic radiation to another wavelength. The present invention includes a method for chemical cleansing of radicals to produce high transparency polymers and a method by which polymer fibers can be made radiation hardened. The present invention includes a method to achieve very rapid polymerization of known monomers. The present invention also includes a method by which a rapid fast cast of polymers is achieved using microwaves and the resulting preform rods can be drawn without the need for degassing.
Plastic or polymer optical fibers have been produced in the prior art over the past several decades. However, the prior art methods of producing the optical fibers have produced fibers that are relatively inefficient with regard to transmission efficiencies, especially when compared to glass optical fibers.
For example, for long-range optical communication a single-mode glass optical fiber has been widely used, because of its high transparency and high bandwidth. In contrast, for short-range communication, recently there has been considerable interest in the development of polymer optical fibers. In short-range communications (such as local area network systems, interconnections, the termination area of fiber to the home, and domestic passive optical network concepts), many junctions and connections of two optical fibers are necessary. In a single-mode fiber, the core diameter is approximately 5-10 micrometers (xcexcm), so when one connects two fibers, a slight amount of displacement, such as a few micrometers, causes a significant coupling loss. The polymer optical fiber is one of the promising possible solutions to this problem, because commercially available polymer optical fiber usually has a large diameter such as 1 mm. Therefore, low transmission loss and high bandwidth has been required for polymer optical fibers to be used as a short-distance communication media.
Most commercially available polymer optical fibers, however, have been of the step-index type. Therefore, even in short-range optical communication, the step-index polymer optical fibers will not be able to cover the whole bandwidth of the order of hundreds of megahertz (MHz) that will be necessary in fast datalink or local area network systems in the near future, because the bandwidth of the step-index polymer optical fibers is only approximately 5 MHz/km.
In contrast, graded-index polymer optical fiber is expected to have a much higher bandwidth than step-index polymer optical fibers, while maintaining a large diameter. Several reports of a graded-index polymer optical fiber have been made by Koike and collaborators (e.g., Ishigure, T., et al., xe2x80x9cGraded-index polymer optical fiber for high-speed data communicationxe2x80x9d Applied Optics Vol. 33, No. 19, pg. 4261-4266 (1994)). However, the methods described in this paper by Ishigure et al., are gel diffusion methods of producing graded index fibers and are cumbersome and expensive.
Traditional methods for making fiber optic polymers include producing fibers either by extrusion or by producing an extrudable preform rod to be drawn in a high temperature oven. In both methods, polymerization processes last for approximately 48 to 72 hours after which polymers are degassed for about 48 to 72 hours to ensure no monomer residuals or other solvents. The entire process may take from 4 to 6 days or longer, thereby hampering large scale production and increasing the possibility of introducing impurities which reduce optical transmission.
What is needed is a low cost and simple method of rapidly producing a graded index polymer optical fiber. What is needed is a method for rapidly producing preform rods with few impurities that does not require a degassing step. The method should produce a low-loss and high-bandwidth graded index polymer optical fiber and should include control of the graded refractive index and flexibility of the fiber. The fiber produced by this method should be flexible. In addition, the method should be easily adaptable to current manufacturing techniques of extruding polymer optical fiber.
The present invention provides for a low-loss and high-bandwidth optical fiber cable that is flexible, rapid, inexpensive, and simple to produce. The present invention also includes methods for producing a graded index preform rod that can be used to make graded index optical fiber cable that is highly flexible. The present invention also provides a method for producing these fibers more quickly and economically than current methods.
For graded index optical fiber cable, the method of the present invention includes beginning with a cylinder of a homogeneous cladding polymer. The cylinder of cladding is inserted into a reaction chamber that is capable of being heated and rotated along its longitudinal axis. For example, the cladding can be a preformed silicone oligomer i.e., xcex1,xcfx89, dichloropropyldimethylsiloxane which has a refractive index of 1.42. Alternatively, microwave radiation may be employed with particular prepolymer compositions to make the preform rod.
A monomer mixture of, for example, the above cladding and excess bisphenyl A polycarbonate with bisphenyl A pyridine methylene chloride solution is then added to the interior of the cladding either continuously or stepwise as the chamber is heated and rotated. Phosgene gas is also added continuously to the chamber as the preform rod is formed. As the copolymer polymerizes on the inner surface of the cladding the proportion of bisphenyl A polycarbonate to dimethylsiloxane can be varied to provide a copolymer with gradually changing refractive index. As the copolymer builds up on the inner surface of the cladding, the amount of polydimethylsiloxane decreases and the amount of bisphenyl A polycarbonate increases until the preform rod is filled in. The preform rod can then be removed from the reaction chamber and used in a conventional extrusion apparatus to manufacture optical fiber.
Another monomer mixture that can be used in practicing the present invention is styrene, methyl methacrylate, and a monomer that polymerizes with lower surface energy polymers, such as fluorinated monomers or siloxane. While not wanting to be bound by the following hypothesis, it is believed that during polymerization, low surface energy polymers migrate outwards, and that the refractive index profile of the preform rod is controlled by the temperature conditions.
The present invention also includes a method for increasing the clarity of the polymer optical fiber by the addition of free radical scavengers such as dibutyl-1-phthalate at a concentration of approximately 0.5% by volume. Other free radical scavengers that can be added to the polymer in the process of producing the preform rod include, but are not limited to, propanol, cyclohexane and butylnitrile. Other agents that can be used to increase the clarity of the polymer optical fiber include, but are not limited to, a variety of low temperature glass transition small molecules, such as siloxane oligomers and different Lewis acids.
The resulting fibers can easily be bundled together and fused by placing the bundle in a container and applying a vacuum to the bundle. The temperature is raised to the glass transition point of the cladding. The bundle is then allowed to cool. The process is desirably repeated several times, preferably four to five times, resulting in a uniform bundle of fibers.
Finally, the present invention includes additives that can be added to any conventional optical fiber and the optical fibers of the present invention that are capable of very large wavelength shifts between the incoming and exiting radiation. Some of these additives produce wavelength shifts include shifts from ultraviolet to blue-green and blue visible radiation. These additives may be added to preform rods, films or other shapes of the optical fibers made with the methods of the present invention.
Accordingly, it is an object of the present invention to provide a graded index polymer fiber optical cable.
It is an object of the present invention to provide a low-loss and high-bandwidth graded index polymer fiber optical cable.
It is further an object of the present invention to provide a method of rapidly manufacturing a flexible, graded index polymer fiber optical cable.
It is further an object of the present invention to provide a method of manufacturing a fused bundle of graded index polymer fiber optical cable.
It is yet another object of the present invention to provide preform rods can be produced rapidly in comparison to previously known methods that require much more time.
It is yet another object of the present invention to provide preform rods and graded index preform rods that can be produced without application of vacuum or a degassing step as required by conventional methods, thereby speeding production of preform rods that are ready to be pulled into fibers.
It is yet another object of the present invention to provide preform rods and graded index preform rods using microwave radiation.
It is yet another object of the present invention to provide an optical polymer suitable for use as a film, gel or fiber optical cable, that is capable of producing large shifts in wavelength between the incoming and exiting electromagnetic radiation.
It is yet another object of the present invention to provide polymers containing the wavelength shifters that can be made in different forms and shapes, and incorporated into radiation surveillance equipment, radiation detectors, and industrial and recreational clothing.
It is another object of the present invention to provide polymer compositions containing the wavelength shifters that can be used for viewing of X-ray, ultraviolet, or infrared radiation as visible radiation. The present invention also includes the shifting of visible radiation to X-ray, ultraviolet, or infrared radiation
It is another object of the present invention to provide polymer compositions containing the wavelength shifters used for viewing of X-ray, ultraviolet, and infrared radiation as visible radiation and to provide the ability to visualize previously invisible radiation in real time and at reduced levels of the incident radiation presently required for visualizing objects, thereby decreasing radiation exposure of patients and health care professionals.
Another feature of the optical polymer fibers of the present invention is that they provide the ability to magnify images with high resolution.
It is another object of the present invention to provide a polymer fiber optical cable suitable for use in endoscopic instruments.
It is another object of the present invention to provide optical fibers that are very flexible.
These and other objects, features and advantages of the present invention will become apparent after a review of the following detailed description of the disclosed embodiments.